The present invention is directed to a thermo transfer printer which has a print head having a plurality of switch cells or elements arranged in a two-dimensional field and controlled by the information to be printed. Energy output from an energy source is transmitted parallel through the switch cells onto the matrix dots, which are arranged in a grid, and these matrix dots lie in the plane of a dye or ink layer on a surface of a bandshaped dye or ink carrier so that portions of the dye or ink will absorb the local energy to a degree to become melted or liquid and be transferred under pressure to the print medium, which is held in contact therewith.
In modern printers, which are preferably utilized as periphery apparatus of data processing systems, non-mechanical printing principles are being utilized to an increasing degree. These principles include printers, which operate on the electrophotographic principle and which have prevailed to a considerable degree. This printing principle is relatively complicated and, thus, costly. This is to be attributed to the fact that an electrostatic image of a print pattern must be generated on a charge drum in order to be able to produce a distribution of the toner particles corresponding to the charge image. Then these toner particles are transferred onto the printed medium, preferably paper, in a single-sheet format or, respectively, continuous form format and are then fixed or secured thereto. Therefore, due to the relatively great technical outlay involved with these devices, there have been many attempts to introduce other non-mechanical printing principles.
One of the other known, even though hereto less successful, non-mechanical printer principles is the principle of thermo transfer printing. In accordance with this principle, a corresponding quantity of energy on the basis of which the production of a matrix dot is initiated, is to be brought locally, for example, micro-points close to or, respectively, on the surface of a print carrier. This can occur, for example, in that special papers are employed which discolor given the incidence of radient energy. An intial disadvantage of this type of printing is the required use of the special papers. Another disadvantage is that the chromatic appearance of the print is restricted. Over and above this, the print quality, for example, the sharpness of the printing produced, also leaves something to be desired given the known thermo transfer printing devices that work with such special papers.
If one wishes to realize the principle of thermo transfer printing without special papers, dyestuff or pigment particles must be transferred in the desired pattern onto the print medium, with the pattern being triggered by locally applied energy. Known solutions for this embodiment of the thermo transfer printing principle cannot satisfy fully, because they are not fully satisfactory in view of the print performance and/or in the print quality as well. Therefore, they cannot compete in competition with known printers, which utilize an electro-photographic principle. Among the reasons for this is that it is difficult to make an adequately high amount of energy for fixing the dyestuff or pigment particles in the matrix dot of a printed pattern available and to also modulate this energy transfer with a corresponding high frequency, which is the prerequisite for a high print performance, but also print quality.
It has become clear, therefore, that two significant problem areas are present in thermo transfer printing. One of these areas is that the ink per se and the way in which the ink is transferred onto the print medium, for this determines the quantity of the energy required. The other problem is the printer head, which is a device with which a momentarily energized image of the desired print pattern is generated close to or at the surface of the print medium. Known printer heads, for example, utilizing heated writing electrodes are in contact with the print medium. They have a problem with a resistance to wear and the thermal inertia of the print element is also a problem. The overall energy required in conventional solutions based on the thermo transfer principle are also high. Known solutions for the utilization of the thermo transfer principle, which have been known for a long time per se have, therefore, always still been unsatisfactory up to now and not adequately competitive in the face of other non-mechanical printing principles so that such a solution has not prevailed.